1. Field of the Invention
The present invention relates generally to electrical component testers and more specifically to a digital controlled bridge for rapidly testing a plurality of types of electrical components and their sequence of presentation.
2. Description of the Prior Art
Most bridge circuits for measuring impedance are modifications of the standard Wheatstone four legged bridge. To balance the potential across the bridge, adjustments are usually made on two of the bridge elements. If the adjustments are known, the unknown impedance can then be calculated from the known impedance and the two known adjustments. A sophisticated system using a computer to drive relays to adjust the bridge to a null is shown in U.S. Pat. No. 3,319,162.
To increase the speed of measurement of a resistance and reduce the amount of parts of mechanization, others have used self-balancing bridges where a resistor under test is connected in a two or four legged bridge with a standard resistance and the signal at the junction between the standard and test resistance is fed back to the voltage applied at one end of the bridge to drive the bridge into balance. The final output of the junction represents the measured percentage of error of the test resistance or device under test to the standard resistance. Two U.S. Pat. Nos. showing this technique are 3,039,050 and 3,139,579. Other attempts of digitally forming a bridge have included the selection from a large plurality of standard resistors, using relay switches, to provide a standard resistor in a two legged bridge with a device under test. The output signal of these digitally controlled bridges is measured against an inputted tolerance signal to provide a pass or fail information. Two U.S. Pat. Nos. showing these type of circuits are 3,065,414 and 3,226,637.
With the increased use of electrical components taped between two pairs of adhesive ribbons for use in electrical component insertion machines of the component, it is important to verify the sequence of components intermixed as to type and value and the value tolerance within a predetermined range. By making the component sequence check on the taped components before feeding them to an insertion machine, time and labor are saved over the complicated testing of the assembled circuit. Additionally, the components do not have to be unsoldered and removed, thus saving time, manpower and money. Two of such mechanized testers are shown by U.S. Pat. Nos. 3,092,253 and 3,629,702. The prior art, as exemplified by the patents discussed above, do not combine the teachings of the prior art to provide a digitally controlled sequenced component tester using a self-balancing bridge for a wide variety of electrical components and including a minimum number of resistor values and mechanical switching.